This invention relates to the field of dispensing of cryogenic liquids, and includes a method and apparatus for dispensing precisely metered droplets of a cryogenic liquid. The invention is especially useful for adding liquid nitrogen to cans or plastic bottles, but it can be used in any other application requiring the controlled dispensing of droplets of a cryogenic liquid.
It has been known to make beverage cans of aluminum, which has the advantage of being light in weight and relatively low in cost. However, aluminum is comparatively soft. It is usually impractical to stack aluminum cans containing a liquid. Unless the liquid in the can is pressurized, as in the case of carbonated beverages, the cans at the bottom of the stack cannot withstand the pressure of the stack and are likely to be crushed. To overcome this problem, it has been known to inject a small amount of a cryogenic liquid, usually liquid nitrogen, into the can, immediately before the can is sealed. The cryogenic liquid vaporizes almost instantly, and expands to many times its original volume. The vaporized cryogen provides the desired internal pressure for the can.
U.S. Pat. Nos. 4,561,258 and 4,592,205 both show systems intended to provide delivery systems for cryogenic liquids, such as liquid nitrogen, for the purpose described above. However, the above patents provide steady streams of nitrogen. They do not generate discrete droplets, so it is not possible to place one droplet of cryogenic liquid into one can, without wasting additional cryogenic liquid.
Another system intended for dispensing liquid nitrogen into beverage cans appears in U.S. Pat. No. 4,588,000. In the latter patent, a rotating rating disk starts and stops the flow of liquid nitrogen into the cans. Vaporized cryogenic liquid helps to halt the flow of the liquid nitrogen after the liquid has been dispensed into a particular can. The latter patent injects small doses of cryogenic liquid into each can, but does not actually produce droplets. Moreover, the latter patent has the disadvantage that the metering/dispensing head requires a moving mechanical part, namely a rotating disk, which opens and closes a flow path for the cryogenic liquid.
Automated equipment exists which makes it possible to move cans or other receptacles through a plant at very high speeds. It is therefore desired to inject discrete droplets of cryogenic liquid into such receptacles, at high speeds, and without wasting significant amounts of liquid.
The present invention produces such droplets in a precise and controlled manner, and makes it possible to inject droplets of cryogenic liquid into receptacles at the rate of about 200-500 receptacles per minute. The apparatus of the present invention can be adjusted to optimize the production of droplets, and provides a reliable means of precisely controlling the flow of droplets of cryogenic liquid.